Question

I have a method that will either return an object or None if the lookup fails. Which style of the following is better?

def get_foo(needle):
    haystack = object_dict()
    if needle not in haystack: return None
    return haystack[needle]

or,

def get_foo(needle):
    haystack = object_dict()
    try:
        return haystack[needle]
    except KeyError:
        # Needle not found
        return None

I’m undecided as to which is more more desirable myself. Another choice would be return haystack[needle] if needle in haystack else None, but I’m not sure that’s any better.

Answer 1

For this particular example, it looks like the dict method get is the most concise:

def get_foo(needle):
    haystack = object_dict()
    return haystack.get(needle)

In general, in Python, people tend to prefer try/except than checking something first – see the EAFP entry in the glossary. Note that many “test for membership” functions use exceptions behind the scenes.

I won’t start a flamewar on the relative merits of multiple returns or the alternatives 🙂